Electric discharge apparatus



March 28, 1961 H. w. VAN NESS ETAL 2,977,529

ELECTRIC DISCHARGE APPARATUS 5 Sheets-Sheet 1 Original Filed Feb. 28, 1955 H Fm 2 6 :22 oucwauow March 28, 1961 H. w. VAN NESS ET AL 2,977,529

ELECTRIC DISCHARGE APPARATUS Original Filed Feb. 28, 1955 3 Sheets-Sheet 2 March 28, 1961 H. w. VAN NESS ET AL 2,977,529

ELECTRIC DISCHARGE APPARATUS 3 Sheets-Sheet 3 Original Filed Feb. 28, 1955 INVENTORS Hubert W. VunNess a William E. Large BY ATTORNEY United States Patent 2,977,529 ELECTRIC DISCHARGE APPARATUS Hubert W. Van Ness, Walnut Creek, Calif., and William E. Large, Lancaster, N.Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania 5 Claims. (Cl. 323-74) Our invention relates to electric discharge apparatus and has particular relation to such apparatus for controlling the operation of an electric resistance welding system. This application is a division of application Serial No. 490,871, filed February 28, 1955, now Patent No. 2,953,678 and assigned to Westinghouse Electric Corporation. In certain of its aspects, this application, like its parent, relates to Patent 2,845,531, granted July 29, 1958; Patent 2,862,151, grant"d November 25, 1958; and Patent 2,802,146, granted August 6, 1957, all to Hubert W. Van Ness, and to our Patent 2,840,686 granted June 24, 1958, all assigned to Westinghouse Electric Coporation, and the above-mentioned application and patents are incorporated in this application by reference.

The welding systems with which our invention concerns itself may be divided into a number of units: a welder or welding machine for engaging the work in a position to be welded, a pow-r supply unit for supplying the welding current to the welder, a solenoid actuating unit for energizing and deenergizing the solenoid of the valve which controls the engagement and the disengagement of the welding electrodes from the work, and a s quence timer for initiating and timing the various functions of the welder; that is, the engagement of the welding electrodes with the work, called squeeze, the transmission of welding current, called weld, the holding of the electrodes in engagement with the work and subsequent disengagement of the electrodes from the work, called hold,

and the resetting called off. A complete operation as described above is called a welding cycle, and each of the functions is called a phase of a welding cycle. The se quence timer includes a circuit, usually called a sequence initiation circuit, for starting the sequence at the beginning of a welding cycle. The sequence initiation circuit usually includes a relay which closes a contact to start the sequence.

In the operation of welding apparatus, particularly in the automotive field, it is customary to produce a large number of welds without interruption. Under such circumstances, the sequence initiation circuit is closed and the sequence timer, and with it the welding apparatus, repeatedly passes through a large number of welding cycles. In welding apparatus, in accordance with the teachings of the prior art of which we are aware, the sequence initiation circuit is of such structure and is so tied into the sequence timer that when the sequence timer is in repeat operation producing a large number of welds without interruption, the starting relay is actuated at the beginning of each welding cycle. We have found that this repeated operation of the starting relay of prior art apparatus markedly deteriorates the relay, and it is an object of our invention to provide a sequence timer including a sequence initiation circuit in which the starting relay shall-not operate repeatedly when the sequence timer is in repeat operation.

It is also desirable in the interest of safety to provide a sequence initiation circuit in which the parts to be ly, and the weld interval is initiated actuated by the operator are subjected only to a low voltage of the order of 20 or 30 volts. Sequence timers in accordance with the teachings of the prior art, including a low voltage sequence initiation circuit, have been of complex and costly structure, and it is another object of our invention to provide a low voltage sequence initiation circuit of simple structure.

The automotive industry in its effort to reduce costs has imposed on welding apparatus the demand that it operate at a high speed. This demand is particularly urgent in the case of gun welders, which it is desired shall produce welds at a rate of as high as 600 per minute. Electronic circuits are available for transmitting signals at rates as high as 600 per minute or even higher, but the availability of such signals from a sequence timer, for example, is not in itself sufiicient to product welds at a high speed. The difficulty resides in the fact that the mechanical components of the guns are not capable of responding instantaneously to signals received from the sequence timer. The practice has then developed in the welding art of transmitting the signals from the sequence timer to the welder so that they anticipate the desired operation of the welder. Specifically, the pratice has developed of transmitting a signal to the solenoid actuating unit of welding apparatus which starts the disengagement of the electrodes from the work before the welding time has elapsed. In accordance with this practice, the hold interval times out before the weld interval, so that before the welding current stops flowing, the electrodes start disengaging the work. The difference between the weld time and the hold time in such operation is called negative hold time. With the concept of negative hold time, a new concept electrode-closed time was introduced to describe the time interval during which the solenoid of the welding apparatus is energized by the solenoid actuating unit. The sequence timers of high speed welding apparatus of the prior art then includes a squeeze component, an electrode-closed time component, a weld component and an off component, and suitably calibrated dials are provided for setting each of the components. In producing welds at a high speed, the squeeze and the electrode-closed time intervals are initiated simultaneousafter the squeeze interval. The negative hold time in such apparatus is equal to the sum of the squeeze and the weld intervals less the electrode-closed time interval. The operator of such apparatus usually desires to set this apparatus for a certain negative hold time, but he cannot make this setting directly by referring to a scale; he must set the squeeze and weld time and the electrode-closed time so that squeeze plus weld less electrode-closed time is the desired negative hold time. There is a tendency to perform this mental operation incorrectly particularly when a changeover is to be made without delay, and it has been found to lead to improper operation of the apparatus.

It is, accordingly, a further object of our invention to provide high speed welding apparatus having facilities for readily setting the negative hold time.

The materials which are welded, particularly in the automotive industry, are of relatively high cost, and it is desirable that every effort be made to minimize loss of material. For this reason, it is another demand of industry, and particularly of the automotive industry, that the welding be stopped promptly, even in the middle of a series of welds, in the event of failure of a critical component, particularly a critical discharge device. The provision for accomplishing this object is called the weld safe provision. The portion of the welding apparatus which is involved in the weld safe provision is usually the discharge device which terminates the how of welding current and its associated circuit. 'It is recognized that if the flow of welding current is promptly stopped in the event of a defect in the apparatus, damage to the material can, to a large extent, be avoided.

Weld safe provisions have been included in low speed welding apparatus, but the practice developed in the case of low speed welding apparatus is not applicable to high speed welding apparatus, and it is a further object of our invention to provide high speed welding apparatus including weld safe facilities which operate etfectively regardless of whether the apparatus is set for positive or negative hold time.

It is further broadly an object of our invention to provide a novel sequence timer for high speed welding.

It is an ancillary object of our invention to provide a novel electronic circuit particularly suitable for use in a sequence timer for a high speed welding system. Another ancillary object of our invention is to provide a novel electronic circuit particularly suitable for use in a solenoid actuating unit having an alternating current solenoid.

in accordance with one aspect of our invention, we provide a sequence initiating circuit fora sequence timer including a transformer having a low voltage primary and a higher voltage secondary. The manually actuable switch for starting the sequence is connected to close the primary circuit. The starting relay is connected to be energized when voltage appears across the secondary.

Once this relay energizes, it closes a circuit which maintainsit energized independently of the starting switch but which opens at the end of each welding cycle and, thus, if the switch is opened after a welding cycle has been started but before it is terminated, the relay reinains actuated. On the other hand, so long asthe manual switch remains closed, the relay remains actuated. Thus, when the apparatus is used to produce a large number of welds continuously and the starting switch 'remains closed during the whole operation, the relay remains closed. The wear and tear on the starting relay by its reopening repeatedly when a large number of welds are being produced without interruption is thus avoided.

In accordance witha further aspect of our invention,

' We dispense with the electrode-closed time, and we provide a sequence timer which, instead of having an electrode-closed time component whichis operated simultaneously with the squeeze component, has a hold component, the timing out of which maybe started simultaneously withithe timing out of the weld component. If the hold timeis to be negative, the hold component may be set to time outbefore the weld, component. The setting is facilitated by providing an auxiliary variable resistor in the hold network which has blank settings at the low end of its range to correspond to the negative hold settings. The adjustable arm of this variable resistor is ganged with theadjustable arm of the variable resistorin the weld network, so that resistance is added by it in the hold networkonly when the variable resistor in the weld network is set'for a higher weld interval than the maximum negative hold time. Under. these circumstances, the hold time, whether it is positive or negative, is set by the main variable resistor in the hold network, and this resistor maybe marked to indicate without any calculation the duration of the negative hold time. i

When the weld network of the just-described apparatus is set fora weldtirne of less than the maximum negative hold time, it affects the negative hold time setting ,so that the latter maybe no greater than the. weld time setting. In accordance with a further aspect of our invention, we provide means for assuring that the negative hold time is independent of the weld time setting even if the latter is less than the maximum negative hold time. Y I I 1 Another aspect of our invention involves the weldsafe feature. In accordance withthi'sa spect of our invention,

we provide a sequence timer having a weld component including a discharge device which is rendered conducting to initiate and maintain the flow of welding current. In addition, we provide a pair of discharge devices both connected to the discharge device of the weld component in such manner that if either of the devices is rendered conducting, the weld discharge device is rendered none conducting and the flow of Welding current is terminated The sequence timer also includes a hold component and an olf component, and the two discharge devices which terminate the weld time are so interconnected with the hold component and the off component that off timing is started only after the hold component has timed out and then only if both of the discharge devices which terminate the weld time are conducting. Thus, if only one of the discharge devices is conducting, the weld time is terminated but the off time is not initiated so that the starting of a new welding cycle is prevented. In addition, the cycling operation following the weld time is started after the hold component has timed out, and, thus, it is immaterial whether the apparatus is operating with a positive or a negative 'hold time.

, In accordance with a still further aspect of our invention, we provide a solenoid actuating unit including a pair of discharge devices which are so interconnected that the operation of the unit may be started from an external signal and when once started, it continues independently of this external signal until stopped by a second external signal. This object is achieved with a circuit in which each of the discharge devices 'is provided with blocking bias which is maintained by the open circuit potential across the other device. If one of the other devices is now rendered conducting, the blocking bias in the other is suppressed, which in turn suppresses the blocking bias of the first to be rendered conducting and thus the two discharge devices mutually maintain each other conducting.

The novel features characteristic of our invention are d'sclosed generally above. The invention itself, both as to its organization and method of operation, together with additional objects and advantages thereof, will be understood from the following description of specific cmbodlments thereof taken in connection with the accompanying drawings, in which:

Figures 1A and 13 together constitute acircuit diagram of a preferred embodiment of our invention.

Fig. 2 i5 8. fragmentary circuit diagram showing a portion of the hold network of the embodiment of our-invention shown'in Figs. 1A and 1B; and

Fig. 3' is a fragmentary circuit diagram showing portions of the weld and hold networks of a modification of our invention. V

Description Figs 1A and 1B 7 I and DL2, which derive their power from the conductors Ll'and L2 through a transformer T1 having a secondary S1 with an intermediate terminal. The conductors AL! and AL3 are connectedto the end terminals of the secondary S1 and the conductor AL2 to the intermediate termia]. The potential between conductors ALI and AL2 is then in opposite phase to the potential between conductors AL3 and AL2. The conductors D L1 and DL'Z-supply directcurrent potential 'ofthehalf-wave type. Thcse conductors are connected,respectively, to conductors ALI and ALQthroughrectifiers 3 and 5. 3

The Weider includes a welding transformer having a primary P and a secondary S. Welding electrodes E1 and E2 are connected across the secondary S. The electrode E2 is actuable by fluid pressure and when so actuated, work W between electrodes E1 and E2 is firmly engaged and subjected to pressure applied to electrode E2.

The Welder also includes the usual fluid line FL, the flow of fluid of which is controlled by a valve V which is normally closed and may be opened by energizing a solenoid VS. The solenoid VS is connected to the Solenoid Actuating Unit and is controlled from the latter. The Welder includes a pressure switch SP which is closed in the Sequence Timer when the pressure between the electrodes E1 and E2 and the work W is adequate for welding.

The Power Supply Unit may be of any suitable type, but is specifically shown as an ignitron contractor. This unit includes a pair of ignitrons I-1 and I-2, each of which has an anode 11, a cathode 13, and an igniter 15. The anodes 11 and the cathodes 13 of the ignitrons I-1 and I-2 are connected in inverse parallel between the conductor L2 and one of the terminals of the primary P of the welding transformer. The other terminal of the primary P is connected to the conductor L1. When the ignitrons I-1 and I-2 are rendered conducting, they supply alternating current through the primary P.

The ignitrons I-1 and I-2 are controlled by a weld relay RW of the sequence timer. This relay RW has a normally open contact 17. Between the cathode 13 and the igniter 15 of each of the ignitrons I-1 and I-2, a pair of rectifiers 19 and 21 and 23 and 25, respectively, are so poled as to conduct positive current from the cathode 13 to the igniter 15. By positive current we mean the flow of ions or so called holes; such ions or holes fiow in a direction opposite to the flow of electrons. The normally open contact 17 is connected between the junction of the rectifiers, and when this contact is closed, firing current flows through a rectifier 19 and 25 or 23 and 21, and an igniter of each of the sets and an associated ignitron I-l or L2 is rendered conducting. The firing current flows at the beginning of a succession of half periods of the supply so that when the contact is closed the ignitrons I-1 and I-2 supply alternating current to the primary P. The Solenoid Actuating Unit includes a pair of electric discharge devices, preferably thyratrons SUT1 and SUT2. Each thyratron has an anode 31, a cathode 33 and a control electrode 35. The anodes 31 and cathodes 33 of the thyratrons SUT1 and SUT2 are connected in inverse parallel in series with the solenoid VS between the conductors L1 and L2. Thus, when the thyratrons SUT1 and SUT2 are conducting, the solenoid VS is energized.

Thyratron SUT1 is supplied with composite control potential made up of three independent components. One of these is derived from a blocking bias network AN1 consisting of a capacitor 37 shunted by a resistor 39. This network AN1 is connected between the control electrode 35 and the cathode 33 of thyratron SUT1 through a grid resistor 41, a resistor 43 across which additional blocking bias is impressed from the Sequence Timer, and a resistor 45 across which counteracting potential is impressed from the Sequence Timer. The terminal of the network AN1 connected to the cathode 33 of thyratron SUT1 is also connected directly to the anode 31 of thyratron SUT2. The other terminal of the network AN1 is connected through a current limiting resistor 47 and a rectifier 49 to the cathode of thyratron SUT2. The rectifier 49 is poled to conduct positive current from the network to the cathode. A resistor 51 is connected between the rectifier 49 and the terminal of the network AN1 which is connected to the anode of thyratron SUT2. It is seen that the network ANl is so connected between the anode 31 and the cathode 33 of thyratron SUT2 that it is charged in a sense to block conduction of thyratron SUT1 by the open circuit potential across the thyratron'SUT2. It follows that when thyratron SUT2 is conducting, the network AN1 is substantially uncharged.

Thyratron SUT2 is controlled only from a network AN2. This network also includes a capacitor 57 shunted by a resistor 54 and is connected between the control electrode 35 and the cathode 33 of thyratron SUT2 through a grid resistor 61. The terminal of the network AN2 connected to the cathode 33 is also connected to the anode 31 of thyratron SUT1. The other terminal is connected to the cathode of thyratron SUT1 through a current limiting resistor 63 and a rectifier 65 poled to conduct positive current from the network AN2 to the cathode 31. A resistor 67 is connected between the rectifier 65 and the terminal of the network AN2 connected to the cathode of thyratron SUT2. Network AN2 is thus charged to a blocking magnitude by the open circuit potential across the thyratron SUT1 and is substantially uncharged when the latter thyratron SUT1 is conducting.

In accordance with the broader aspects of our invention, the Sequence Timer may be of any type known in the art, such for example, as the timers shown in Patents 2,862,151 and 2,802,406 mentioned above, but specifically the Sequence Timer is an adaptation of the timer shown in the above-mentioned Patent 2,845,331.

The Sequence Timer includes a low voltage sequence initiation circuit, a plurality of thyratrons including an off thyratron OT, a squeeze thyratron ST, weld thyratrons WT1, WT2, and a hold thyratron HT for controlling the various functions of the Welder; a plurality of networks including the off network ON, the squeeze network SN, the weld network WN, and the hold network HN for timing the various functions of the Welder. The Sequence Timer also includes a plurality of auxiliary thyratrons ATl, AT2 and AT3 for producing transitional operations of the sequence timer and a plurality of auxiliary net-' works AN3, AN4, ANS and AN6. The Sequence Timer further includes a start switch SS, a start relay RS, the weld relay RW, a repeat-non-repeat switch SW1 and a switch SW2 for setting the apparatus either for positive hold during low-speed welding or for negative hold during high-speed welding. The switch SS may be the foot switch of a press welder or the trigger of a gun Welder.

The sequence initiation circuit includes a transformer LT having a low-voltage primary LP and a higher voltage secondary LS. The transformer LT is designed to supply the higher voltage across the secondary LS which is necessary for the operation of the relay RS with a potential of the order of twenty-four volts across the primary LP. The sequence initiation circuit is energized from a transformer T2 having a primary connected across the conductors AL1 and AL2, the secondary S2 of this transformer supplies a low voltage of the order of twenty-four volts. The primary LP and the secondary S2 are connected in a normally open series circuit through the start switch SS.

The higher voltage secondary LS is connected across the coil of the starting relay RS through a rectifier 71 poled to conduct positive current from the coil of the relay to the secondary LS. The relay RS has a normally open contact 73 which, when closed, connects a conductor AL4 to the conductor AL2, Since the coil of the relay RS draws only half-wave current through the rectifier, it may be desirable to connect across this relay a rectifier 75. The rectifier 75 is poled to conduct current in a direction opposite to the direction of the energizing current through the coil.

The sequence initiation circuit cooperates with the off thyratron OT which has an anode 81, a cathode 83 and a control electrode 85. The anode 81 of thyratron OT is connected to the conductor DL 1 through the primary AP1 of a transformer AZ1. The cathode 83 is connected to the conductor AL4. The anode of thyratron.

OT is also connected through anotherrectifier 87 to the junction of the coil of relay RS and the rectifier 71 in series with it and the secondary LS. The rectifier 87 rectifier 75 connected between the coil and the secondary The secondary AS1 of the-transformer AZl is connectedvacross the resistor 45 in the control circuit of thyratron SUT1 through resistor 91 and rectifier 87, and when current is conducted by primary APlof transformer All, a potential is impressed across the resistor 45 which counteracts the blocking potential impressed by the network ANl.

The off network-ON includes a capacitor 97 shunted by a fixed resistor 99 and a variable resistor 101. The variable resistor 101 may be shunted out by a contact 103 of the repeat-non-repeat switch SWlwhen the latter is in the non-repeat position. Under such circumstances, the capacitor 97 may be discharged in a short interval of the order of a period of the supply. The off network ON is connected between the control electrode 85 of the thyratron OT and theconductor AL2, through a grid resistor 105 and the secondary A52 of another transformer AZ2. A resistor 107 and a rectifier 109 are con-' nected between conductors ALI and AL2 and have a junction J1. Junction J1 is adapted to be connectedto the anode 81 through the pressure switch SP.

The squeeze thyratron ST has an anode 115, a cathode 113 and a control electrode 111. The squeeze netagrid resistor 123 and the squeeze network SN. As is explained in the application, Serial No. 424,094, and the applications to which it relates the purpose of the connection to the junction I1 is to reduce the negative potential'on thecontrol electrode 111 of thyratron ST whenv it is being rendered non-conducting and thus to preventgas clean-up in this thyratron.

The weld thyratrons WTl and WT2 are similar. Each.

has an anode 131, a cathode 133 and a control electrode 135. The network WN consists of a capacitor 137 shunted by.v a fixed resistor 139 and variable resistor 141. The anode 131 of thyratron WTl is connected to conductorDLl The anode of.

through the primary AP4 of a transformer AZ4. The;

cathode 133 is connected to the conductor AL4. anode 131 of the thyratronWTZ is connected to the conductor DL1 through the primary AP5 of a transformer AZS. The cathode 133 is connected to the conductor AL2. Control potential for the thyratrons WTl and WT2 is derived from the junction J2 of a rectifier .143

The.

cuited out over the range corresponding to the maxiinum negative hold time which it is desired be used. Thus,

assume,.for example, that the capacitor 167 andthe.

variable resistors 171 .and 173 are so related that. 10,000 ohms in the'network HN correspond to a time interval of one full period, and that the maximum negative hold timeis four periods.

resistor 171 is shorted out.

. In the negative hold setting of the Sequence Timer,

the adjustable arm 177 of the variable resistor 173 adds no resistance in the hold network HN while thisarm and the arm of the variable resistor 141 in the weld network.

are moving from a point correspondingto zero weld time to a'point corresponding to four periods weld time. The

negative hold time may then be set by setting the other.

variable resistor 171 in the hold. network HN, the setting near the lower portion of its range corresponding tonegative hold time and the settingsin the remaining portion.

of its range corresponding to positive hold time as shown in Fig. 2. When the variable resistor 141 inthe weld network WN is set for higher weld time than the maximum negative hold time, the variable resistor 173 in the hold network HN ganged with the resistor 141 adds resistance in the hold network HN corresponding to that added in the weld network, and thus, the setting of the other variable resistor 171 in the hold network still determines the.

magnitude of the negative or positive holdtime. Thus, assume thatthe variable resistor 141 in the weld network WN is set for six periods weld time and the variable resistor 171 in thehold network HN is set for minus two periods holdtime. The ganged variable. resistor 173 in the hold network HN is then set for two periods hold time so thatthe total hold time inthe hold network HN is four periods, and this is two. periodsless than the settingof the weld network WN so that the negative hold time is two periods. V

The anode'lfil of the hold thyratron HT is connected to the conducter DL1 through theprimary AP6 of' a to conduct positive current to the junction J 4. The anode and a resistor 145 connected between the conductors AL3 I anode 115 of thevsqueeze thyratron ST. Between. the.

anodes of the thyratrons WT1 and WT2 and a junction J3 a pair of rectifiers 149and 151 are connected, each rectifier being poled to conduct positive current from its associated anode to the junction I3.

The hold thyratron HT has an anode 161, a cathode 163, and a control electrode 165. The hold network EN 161' is also connected to thejunction 16 of a resistor 188 and a rectifier 190 connected between conductor ALI and conductor AL2. Control potential for the thyratron HT is derived either through a contact 189 of the negative hold switch SW2 from the junction J5 of a resistor 191 and includes a capacitor 167 shunted by a fixed resistor 169,

a variable resistor 171, an additional variable resistor 173 which may be shunted out by a contact 175 of the negative hold switch SW2 when the latter is set for positive hold. The resistor 171 may be of the type shown in Fig. 2 which has a scale marked nearthe low resistance I end for. negativehold. t

It is'now desirable to digress for the purpose ofjdescribing'the components of the weld and hold networks WN and .HNandtheir relationship. The'adjustable arm .177 ofr thelatter variable resistor173 is ganged with the adfju sta'ole arm 179 of the variable resistor 141,in;theweld. networ k WN.L,- The low,resistanceiportion. 181 oi-rthe. variable resistor 173 in the hold network HN is short cira rectifier 193 connected between the conductors AL3 and AL2 or from the junction J2 if the switch SW2 is in the negative hold position. The junction 15 or I2 is connected to the control electrode through the contact 189 of the switch SW2, through the hold network vHN and through a grid resistor 195. i

The thyratron ATl has an anode 201, a cathode 203 and a control electrode 205. The network AN3 consists of a capacitor 207 shunted by a resistor 209. The network 'AN4 consists. of a capacitor-217i shunted by apair .of resistors 219 and 221. Across the network AN3, the

Thelanode 201,-of .thyratron.AT1 is. connected to the conductor. AL3 through the coil'of therelay RW.

cathode 203 is connecteditoQtheconductor .ALZL The control electrode 205 of'thyratron 'ATfisconnected:

Under such circumstances, the first 40, 000 ohms from. the zero ohm terminal of the variable.

9. through a grid resistor 225, the network AN3, the secondary AS3 of the transformer A23 and the network AN4 to the conductor AL2. In this circuit the network AN4 is charged to such a potential as normally to block the conduction of thyratron AT1. The secondary A83 is so connected that when the thyratron ST conducts, potential is impressed through the secondary A53 to counteract the blocking potential of the network AN4. The primaries A84 and AS are so connected that when either thyratron WTl or thyratron WT2 conducts or both conduct, sufficient potential is impressed across the network AN3 to block the conduction of thyratron AT1 even if potential is available across the secondary A53.

The thyratron AT2 has an anode 231, a cathode 233 and a control electrode 235. The network ANS consists of a capacitor 237 shunted by a resistor 239, the relationship between the capacitor 237 and the resistor 239 being such that the capacitor when charged and permitted to discharge, discharges substantially in a time interval of the order of one period of the supply. The anode 231 of thyratron AT2 is connected to the conductor DL2 through a reactance 241 sufiicient to produce carry-over in the conduction of thyratron AT2. The cathode 233 is connected to the conductor AL2. The control electrode is connected through a grid resistor 245 and the network ANS to the junction J3.

Thyratron AT3 includes an anode 251, a cathode 253 and a control electrode 255. Network AN6 includes a capacitor 257 shunted by a resistor 259 and has a time constant similar to network ANS. The anode 251 of thyratron AT3 is connected to conductor DL2 through the primary AP2 of the transformer AZ2. The cathode 253 is connected to conductor AL2. The control electrode 255 is connected through a grid resistor 261 and network AN6 to the junction J4.

Stand-by-Figs. 1A and 1B In the stand-by condition of the apparatus, the disconnects or circuit breakers (not shown) for the apparatus are closed and conductors L1 and L2 are energized. Power is then supplied to the apparatus and the cathodes of the various thyratrons are heated so that they can conduct if proper potential is applied tothem. The start switch SS is open and there is no potential across the secondary LS and relay RS is deenergized so that the connection between conductors AL2 and AL4 is broken. Thyratrons OT, WT1 and HT are then nonconducting and transformers AZ1, AZ4, AZ5 and AZ6 are deenergized. There is then no potential across secondary A53 and networks AN1 and AN2 become charged by the open circuit potential across the thyratrons SUTZ and SUTl and these thyratrons are non-conducting. The valve solenoid VS is then deenergized, the valve V is closed and the electrode E2 is retracted from electrode E1.

During the half periods when conductor ALI is positive relative to conductor AL2, network SN is charged by grid conduction through thyratron ST. During the other half periods the charge on this network maintains thyratron ST non-conducting. Transformer AZ3 is then deenergized and thyratron AT1 is non-conducting. Relay WT is deenergized and ignitrons 1-1 and 1-2 are non-conducting.

The network WN is similarly charged by grid conduction through thyratron WT2 during the half periods during which the conductor AL3 is positive relative to conductor AL2. Thyratron WT2 is then also nonconducting.

Network 'HN is connected at one terminal to conductor AL3 either through junction'l2 or through junction J5, depending on the-position of the negative hold switch SW2. It is connected at the other terminal to the control electrode of thyratron, but since the cathode return of this thyratron is connected to the open conductor AL4, thereis no potential impressedacross network HN. The

network is then uncharged. Thyratron HT is, however, non-conducting because its cathode return circuit is open.

Network AN6 is connected to the junction J 6 through junction J4 and the rectifier 187 to the other terminal between the control electrode and the cathode. This network is then charged so as to maintain thyratron AT3 non-conducting when conductor AL1 is positive relative to conductor AL2. With thyratron AT3 non-conducting, transformer A22 is deenergized, network ON is discharged and thyratron OT, while non-conducting because its cathode return is open at contact 73, is ready to conduct immediately on the closing of this cathode return.

Operation Figs. 1A and 1BRepeat-P0sitive hold The operation of the apparatus shown in Figs. 1A and 1B will now be explained with the repeat-non-repeat switch SW1 set for repeat and the switch SW2 set for positive hold, that is, in the position shown in the drawings. Since the switch SW1 is set for repeat, the apparatus will be described on the assumption that a plurality of welds are to be produced.

To produce a plurality of welds, the work W is disposed on electrode E1 and the start switch SS is closed. The low voltage primary LP is then energized and poten-- tial is supplied to the secondary LS. Current then flows through the coil of the start relay RS and the latter picks up, connecting conductor AL4 to the energized conductor AL2. Current then immediately flows through thyratron OT. This current flow has two parallel paths, one through the primary APl and the other through the relay RS. The relay RS is then maintained actuatedthrough thyratron OT so long as it remains conducting. The relay RS is also maintained actuated by the current derived from the primary LS so long as the switch SS remains closed. Thus, once the thyratron OT is rendered conducting, the relay RS remains actuated regardless of whether or not the operator opens the switch SS and the apparatus has the so-called non-beat property, that is, a welding cycle can not be interrupted before it has been completed. On the other hand, during repeat welding, the switch SS remains closed for the whole series of welds and the relay RS remains actuated and does not repeatedly open and reclose as the thyratron OT becomes conducting and non-conducting.

The closing of the contact of relay RS also completes the anode-cathode circuit for thyratron HT. The network HN in the control circuit of thyratron HT is uncharged, but unlike thyratron OT, thyratron HT is not rendered conducting. This can be understood by considering the relationship of the control and anode potentials on thyratron HT under the alternative conditions which might exist on the closing of the contact 73 of the relay RS, that is, when at the instant when the contact 73 closes the conductor ALl, and the conductor DLl, is positive relative to the conductor AL2, and when the conductor AL3 is positive relative to the conductor AL2. In the case of the first alternative, thyratron HT does not conduct because its control electrode is connected through the uncharged network HN to the conductor AL3 which is, at the time, highly negative with respect to conductor AL4 and the cathode 163. In the case of the second alternative, thyratron HT can not conduct because there is a negative potential impressed between its anode and its cathode, but the network HN is charged to its timing potential by grid current flowing through thyratron HT under the potential diiference between conductor AL3 and conductor AL2.

On the supply of current through the primary APl, potential appears across the secondary A5 1 and across the resistor 45 in the control circuit of thyratron-SUTL Thyratron SUTl is then rendered conducting and a half cycle of current flows through thesolenoid -VS.' On the conduction of thyratron SUTl the charge delivered to the network AN2 during'the half period during- 11 thyratron SUTl conducts is small. The magnitude of resistor 54 is such that the network discharges sufficiently to permit thyratron SUT2 to conduct when the anodecathode potential of the latter becomes positive. An-

other half cycle of current now flows through the solenoid VS. Since thyratron SUT2 is conducting during this last half period, network ANl accumulates only a very small charge and permits'thyratron SUTl to conduct again during the succeeding half period independently of any potential on transformer AZ1. Thyratron SUTl then conducts again. This conduction of thyratrons SUTl and SUT2 in succession now continues, each permittingthe other to conduct, and current flows through the solenoid'VS and the valve V is opened, causing the electrode E2 to engage the work W1. When adequate pressure has been applied to the electrode E2, the switch SPfis closed.

The closing of the switch SP connects the anode of thyratron OT to the junction J1, reducing the potential for. charging the squeeze network SN and permitting it to discharge. When network SN has timed out, squeeze thyratron ST is rendered conducting, supplying current through the primary AP3. Potential appears across the secondary A83, and this potential counteracts the blocking potential impressed by the network AN4, and thyratron AT1 is rendered conducting.

Relay RW is then energized to close the welding contact 17 through the starting circuits of ignitrons I1 and I-Zand the latter conduct. Current now flows through the primary P and as a result through the work W to produce the desired weld.

The conduction of thyratron ST also reduces the charging-potential for the network WN and'the latter discharges. The network WN is set so that the weld interval persists for a sufficient time to provide a sound weld. When network WN times out, thyratrons WT1 and WTZ conduct. If these thyratrons and their circuit is in proper operating condition, both thyratrons WT1 and WT2 will conduct. Under the circumstances, both transformers A24 and AZS .are energized and potential is impressed across network AN3' to counterbalance the potential impressed by secondary AS3. Thyratron AT1 is then again rendered non-conducting, the weld relay RW is deenergized and the flow of current through the welding transformer T and through the work W is interrupted. The potential impressed across the secondaries A84 and AS5 is such that even if one of the thyratrons WT1 or WTZ does not conduct, the thyratron AT1 is still rendered non- WT2 are both conducting and the other, that WT1 or.

WT2 is conducting, need now be considered; If both WT1 and WT2 are conducting, the potential for charging network ANS through junction J3 is reduced and the network ANS discharges, permitting thyratron AT2 to conduct. The conduction of thyratron AT2 reduces the charging potential for network HN and the latter is permitted to discharge continuing the sequence. If only thyratron WT1 or thyratron WTZ is conducting, there is chargingpotential supplied to junction J3 through the rectifier 149 or 151 connected to the anode'131 of the nonconducting thyratron. Network ANS then. remains charged and thyratron AT2 remains non-conducting. Network HNthen remains charged and the continuation of the sequence is interrupted until the apparatus 'is repaired. t 7

Now the'explanationof the sequence may be continued, assumingthat thyratrons'WTl and WTZ are both conducting. Under-such circumstances, network ANS dis-.

charges rendering thyratron AT2 conducting and the hold;

circuit of thyratron SUTl. This, potential is so poled as to impress a blocking potential on thyratron SUTI, to render it non-conducting. Once thyratron SUTl is rendered non-conducting during a -half period, the network AN2 is charged during the same half period to block thyratron SUT2, which in turn, permits the network AN1 to charge to block thyratron SUTl. The flow of current through the solenoid VS is then interrupted, the valve V is closed and the electrode E2 is permitted to retract from thework W and switch SP is opened. The network HN is usually set so that it times out only after the weld has solidified.

In addition, the potential at junction I4 is now reduced, and this, in turn, reduces the charging potential for network AN6. The latter discharges so as to permit thyratron AT3 to conduct in a time interval of the order of one period of the supply. The conduction of thyratron AT3 energizes transformer AZ2 and network ON is charged. The charging of network ON impresses a blocking potential on thyratron OT and the latter is rendered nonconducting. If the start switch SS is held closed, as it would be during a repeat operation, this does not affect the relay RS whichremains closed because of the potential impressed across the secondary LS.

The junction I1 is raised in potential either by the nonconduction of the thyratron OT or the opening of switch SP whichever occurs first and network SN is charged. The charging of network SN renders thyratron ST nonconducting and transformer AZ3 is deenergized, removing the potential across secondary AS3. This has no immediate effect since thyratron AT1 is maintained non-' conducting by the potential impressed by transformers A24 and AZS.

But the non-conduction ofthyratron ST has another effect, it provides charging'potential for network WN which immediately charges to render thyratrons WT1 and WT2 non-conducting. Transformers AZ4 and A25 are then deenergized, but this has no immediate effect be-.

cause transformer AZ3 is already deenergized, and network AN4 is efi'ective to maintain thyratron AT1 nonconducting.

The non-conduction of thyratrons WT1 and WTZ pro-- vides charging potential for network ANS which immediately charges, rendering thyratron AT2 non-conducting. The non-conduction of this thyratron provides charging potential for network HN rendering thyratron HT nonconducting. The supply of potential through secondary A86 to the control circuit of thyratron SUTl is now interrupted, but thyratron SUTl remains non-conducting because there is no energizing potential available across secondary ASl, thyratron OT being non-conducting.

The non-conduction of thyratron HT provides charging potential for network AN6 which immediately charges, rendering thyratron AT3 non-conducting. Transformer AZ2is now deenergized, permitting network ON to discharge. Network ON' discharges dun'ng the OE interval, giving the operator suflicient time to move the Work to the position of the next weld, and thenthyr'atron OT'is.

Operation Figs. 1A and 1BP0sitive hold--non-fepedt With the switch SW1 setin the non-repeat position, the anode of thyratron AT3 is connected to the weld network WN through a contact301 of the switch and a rectifier 303 poled to conductfrom thenetworkWN to thexanode. 'In addition the network ON is set totime out an interval ofthe order of a period of the supply.

7 With. the switch SW1 in the 'non-repeatposition, the.

operation after theclosing of the switchSS is thesame as with. the switch :in, the: repeat; position, ,except that.-

rendered conducting, it reduces the potential of junction J2 so as to prevent network WN from being charged, and thyratrons WT1, and WT2 are maintained conducting. With thyratrons WT1 and WT2 conducting, thyratron ATZ remains conducting, maintaining network HN uncharged and thyratron HT conducting so that thyratron AT3 is maintained conducting. The conduction of thyratron ATS also energizes transformer AZ2 so that network ON is charged and thyratron OT remains nonconducting, but this has no effect on the relay RS, and thus, on the thyratrons WT1 and HT so long as switch SS remains closed. To reset the apparatus, the switch SS must be opened, relay RS then becomes deenergized, deenergizing conductor AL4 and permitting thyratron HT to become non-conducting. This, in turn, charges network AN6 causing thyratron AT3 to become nonconducting and resetting thyratrons WT1, WT2 and AT2. The apparatus is now reset for another operation which may be started by reclosing the start switch SS.

Operation Figs. 1A and lB-Negative hold-Repeat When the apparatus is to be operated at a high speed, the switch SW2 is set for negative hold and the switch SW1 for repeat. In this case, the network HN is connected to junction J2 so that it starts timing out at the same time as the weld network WN. In addition, the network HN is disconnected from the junction J5 so that it is not affected by the conduction ornonconduction of thyratron AT2. Further, the short circuit across the auxiliary variable resistor 173 in the network HN is opened so that it becomes effective and permits the negative hold time to be set alone by the other variable resistor 171.

The operation following the closing of switch SS is the same as for positive-hold-repeat up to the point where thyratron ST is rendered conducting. At this point, thyratron AT1 is rendered conducting, energizing relay RW, which in turn closes the starting circuits through the ignitrons I-1 and I-2 causing welding current to flow through the work. In addition, the timing out of the networks HN and WN starts.

Since the apparatus is set for negative hold, network HN times out first, rendering thyratron HT conducting. Thyratrons SUTl and SUT2 are then rendered nonconducting to close valve V and permit the electrode E2 to be retracted from the work W. This operation takes a short time interval and during this interval network WN is still timing out and welding current is still flowing.

Network WN actually times out a short time interval after network HN. Thyratrons WT1 and WT2 are then rendered conducting if they and their circuits are in operating condition, and thyratron AT1 is rendered nonconducting, the weld relay RW is deenergized and the flow of welding current is stopped.

If both thyratron WT1 and thyratron WT2 are conducting, network AN6 discharges permitting thyratron ATS to conduct, the latter charges network On to render thyratron OT nonconducting. By this time the electrode E2'has retracted from the work W and network SN is permitted to charge because the switch SP has opened and thyratron OT has become nonconducting. Thyratron ST then becomes nonconducting, permitting networks WN and HN to recharge. to render thyratrons WT1, WT2 and HT nonconducting. Network AN6 then charges, rendering thyratron AT3 nonconducting, permitting network ON to discharge. Thyratron OT is then again rendered conducting to start another welding cycle.

If thyratron WT1 or thyratron WT2 or their circuits are defective, network AN6 remains charged when one or the other of the thyratrons WT1 or WT2 becomes conducting. Thyratron AT3 then remains nonconducting, and thyratron OT conducting, to prevent another Weld cycle until the apparatus is repaired.

Description Fig. 3

The indicating facilities for the welding system shown in Figs. 1A and 1B is satisfactory when the weld time is set to exceed the maximum negative hold time, but is not entirely satisfactory when the weld time is set for less than the maximum negative hold time. Thus, with reference to the apparatus shown in Figs. 1A and 1B, assume that the maximum negative hold time is four periods and that the weld time is set for five periods. Also assume that three periods negative hold time is desired. Under such circumstances, the resistance in the weld network WN is such that the network times out in five periods. The resistance in the hold network includes one period resistance on the main variable resistor 171 and one period resistance on the auxiliary variable resistor 173. The total then is two period resistance and the hold network HN times out in two periods so that there is a total negative hold time of three periods. Now assume, with reference to Figs. 1A and 1B, that the weld network WN is set for three periods and the main variable resistor 171 in the hold network HN for a negative hold time of three periods. Under such circumstances, the weld network WN has suflicient resistance to time out in three periods but the hold network has resistance corresponding to one period and times out in this one period. The negative hold time is then not three corresponding to the setting but only two.

This deficiency is corrected in the Fig. 3 modification. This modification is similar to the modifications shown in Figs. 1A and 1B, but in addition, includes a switch SW3 ganged with the variable resistor 141 in the weld network WN and the auxiliary variable resistor 173. The switch SW3 with an extended brush or contact 501 short circuits any resistance of the variable resistor 171 in the hold network HN at the beginning of its range which would increase the hold time beyond the weld time setting. In addition in this modification of our invention, the secondary AS3 (Fig. 1A) is so poled as to render thyratron AT1 conducting one period after thyratron ST is rendered conducting so that the timing out of the weld and hold times starts one period before the start of the welding current. The scale of the resistor 141 should then be marked to correspond to the number of periods of actual welding current, that is, the lowest setting of the switch should be labelled zero be cause at this setting the weld network times out in one period and thus before there is any welding current.

Under such circumstances, when, as in the above example, the weld network WN is set for three periods and the hold network for minus three periods, the total resistance in the weld network WN is such that it times out in four periods and the resistance in the hold network HN corresponding to one period is shorted out by the ganged switch SW3 so that the hold network times I one period after the conduction of thyratron ST. But

the weld current starts one period after the start of the timing out of the hold network and times out three periods after this. Thus the weld exceeds the hold by three periods as required.

Conclusion From the above description it is seen that we have invented novel welding apparatus for welding either at low speed or at high speed. This apparatus includes a weld safe feature which operates independently of the setting of the apparatus for positive hold time or negative hold time. Our invention also includes certain novel circuit combination which we conceived in arriving at a solution of the broad objects of our invention. While we have described certain specific embodiments of our invention, many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art.

15 We claim as our invention: 1. In a'sequence timer forhigh'speed welding,'wliich timer is capable of being set to operate with a predetermined maximum negative hold time, a weld network' including a timing impedance element and a first variable resistor having an adjusting arm cooperative with said element to time weld time, the weld time increasing as the resistance of said first resistor increases, a hold network including in series a second variable resistor and a third variable resistor, each having an adjusting arm, and also including a timing impedance element cooperative with said second and third resistors to time hold time, the hold time increasing as the aggregate resistance of said second and third resistors increases, and means ganging' the adjustable arms of said first and second resistors, said arms being adjustable to corresponding settings on said first and second resistors when so ganged, and said second resistor having substantially zero resistance over the range of its resistance corresponding to said predetermined negative hold time.

2. In a sequence timer for high speed welding, which timer is capable of being set to operate with a predeten' minedmaximum negative hold time, a weld network including a timing impedance element and a'first variable resistor having an adjusting arm cooperating with said element to time weld time, the weld time increasing'as the resistance of said first resistor increases, a'hold network including in series a second variable resistor and a third variable resistor, each having an adjusting arm, and also including a timing impedanceelement cooperative with said second and third resistors to time weld time, the

hold time increasing as the aggregate resistance of said second and third resistors increases, means gauging the adjustable arms of said first and second resistors, said arms being adjust-able to corresponding settings on said first'and second resistors when so ganged, and said second resistor having substantially zero resistance over the range of its resistance corresponding to said predet'er I mined negative hold time, and switch means having an actuating arm ganged with the adjustable arms of said necting said first and second varying means to operate thereof cooperative with said element to time weld time,

the weld time increasing as the impedance of said first impedance increases, a hold network including in series a second variable impedance having second means for varying the impedance thereof and a third variable impedance having third means for varying the impedance thereof, and also including a timing impedance element cooperative with said second and third impedance to time weld time, the hold time increasing as the aggregate imfirst and secondresistors for shunting out resistance in the 7 low resistance range of said third resistor which, when said first and second resistors are set for a time interval less than the maximum negative hold time, corresponds to the magnitude by which said maximum negative hold time exceeds said time interval.

3. In a sequence timer for high speed welding, which timer is capable of being set to operate with a predetermined maximum'negative hold time, a weld network including a timing impedance element and a first variable resistor having first means for varying the resistance thereof, the weld time increasing as the'resistance of said first resistor increases, a hold network including in series a second variable resistor having second means for I varying the resistance thereof anda third variable resistor having third means for varying the resistance thereof, and also including a timing impedance element cooperative with said second and third resistors to time 'weld time, the hold time increasing as the aggregate resistance of said secondand third resistors increases, and means conpedance of said second and third impedances increases, and means connecting said first and second varying means to operate together to set said first and'second impedances in corresponding settings, said second impedance having substantially zero impedance over the range of its im-- pedance corresponding to said predetermined negative hold time.

5. In a sequence timer for high speed welding, which timer is capable of being set to operate with a predeter mined maximum negative hold time, a weld network including a timing impedance element and a first variable impedance having first means for varying said impedance cooperative'with said element for timing weld time, the weldtime increasing as the impedance of said first impedance increases, a hold networkincluding in series a second variable impedance including second means for varying the impedance thereof and a third variable impedance, including third means for varying the impedance thereof, and also including a timing impedance element cooperative with said second and third impedance to time hold time, the hold time increasing as the aggregate impedance of said second and third impedances increases, means connecting'said first and second varying means to operate together to set said second and third impedances to corresponding settings together, said second impedance having substantially Zero impedance over'the range ofits impedance corresponding to said predeterminedn'egative hold time, and switch means connected to said connecting means and operable therewith for shunting out impedance in the low impedance range of said third impedance'which, when saidjfirst and secondimp edances are set for a time interval less than the maximum negative hold time, corresponds to'the magnitude by which said maximum negative hold time exceeds 7 said time interval.

" Reference's'Cite'd in the file of this patent UNITED STATES PATENTS 

